Formation of complex Frank–Kasper spherical phases from the self-assembly of block copolymers has attracted renewed interest. In this work, we have studied the emergence and stability of the Laves phases (C14 and C15), belonging to the class of Frank–Kasper phases, in the binary blend of AB4 miktoarm star block copolymers and A-homopolymer using self-consistent field theory. Neat AB4 copolymer with a large conformational asymmetry exhibits a large spherical phase region consisting of four different spherical phases: the face-centered-cubic (FCC), body-centered-cubic (BCC), and Frank–Kasper σ and A15 phases. In contrast, the addition of A-homopolymers into AB4 copolymers leads to the formation of new Frank–Kasper phases, i.e., the Laves phases of C14 and C15. Our work unveils that the Laves phases with more nonuniform domains than the σ and A15 phases are mainly stabilized by the redistribution of A-homopolymers among different A-domains that reduces the interfacial energy between the A-homopolymers and the B-blocks of AB4. At the same time, it implies that the conformational asymmetry should not be necessary for the formation of the Laves phases.

Quasicrystalline (QC) phases have been observed in various condensed matter systems including self-assembling block copolymer (BCP) melts. Theoretical study of the thermodynamic stability of QC phases presents a long-standing unsolved problem because of the aperiodic nature of the structures. Here, we report a combination method to study the thermodynamic stability of two-dimensional dodecagonal quasicrystalline (DDQC) phase with both ideal tiling and random tiling patterns formed by ABCB tetrablock terpolymers. This method applies the self-consistent field theory coupled with the Stampfli self-similarity construction to accurately calculate the free energy of the periodic DDQC approximants and then uses a cluster model to predict the stability of aperiodic DDQC phase. Surprisingly, we find a stable DDQC approximant but metastable ideal tiling DDQC structures. Moreover, the random tiling DDQC structures as a mesoscopic coexistence of two neighboring periodic substructures of DDQC might become stable.

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The complexes formed by DNA or siRNA interacting with polycations showed great potential as nonviral vectors for gene delivery. The physicochemical properties of the DNA/siRNA complexes, which could be tuned by adjusting the characteristics of polycations, were directly related to their performance in gene delivery. Using 21 bp double-stranded oligonucleotide (ds-oligo) and two icosapeptides (with the repeating units being KKGG and KGKG, respectively) of the same charge density as model molecules, we investigated the effect of charge distribution on the kinetics of complexation and the structure of the final complexes. Even though the distribution of the charged groups in peptides was only adjusted by one position, the complexes formed by (KKGG) 5 and ds-oligo were larger in size and easier to precipitate than those formed by (KGKG) 5 . Counterintuitively, it was not the charged groups but the hydrophilic neutral spacers that determined the kinetics and the structure of the complex. We attributed such an effect to the water-mediated disproportionation process. The hydrophilic spacers next to each other were better than that in the separated pattern in holding water molecules after forming the complex. The water-rich domains in the complex functioned as a lubricant and facilitated the relaxation of the polyelectrolyte, resulting in a fast complexation process. The resulting complex was thus larger in size and lower in surface energy.

Complexation behavior of oppositely charged polyelectrolytes in a solution is investigated using a combination of computer simulations and experiments, focusing on the influence of polyelectrolyte charge distributions along the chains on the structure of the polyelectrolyte complexes. The simulations are performed using Monte Carlo with the replica-exchange algorithm for three model systems where each system is composed of a mixture of two types of oppositely charged model polyelectrolyte chains (EGEG)5/(KGKG)5, (EEGG)5/(KKGG)5, and (EEGG)5/(KGKG)5, in a solution including explicit solvent molecules. Among the three model systems, only the charge distributions along the chains are not identical. Thermodynamic quantities are calculated as a function of temperature (or ionic strength), and the microscopic structures of complexes are examined. It is found that the three systems have different transition temperatures, and form complexes with different sizes, structures, and densities at a given temperature. Complex microscopic structures with an alternating arrangement of one monolayer of E/K monomers and one monolayer of G monomers, with one bilayer of E and K monomers and one bilayer of G monomers, and with a mixture of monolayer and bilayer of E/K monomers in a box shape and a trilayer of G monomers inside the box are obtained for the three mixture systems, respectively. The experiments are carried out for three systems where each is composed of a mixture of two types of oppositely charged peptide chains. Each peptide chain is composed of Lysine (K) and glycine (G) or glutamate (E) and G, in solution, and the chain length and amino acid sequences, and hence the charge distribution, are precisely controlled, and all of them are identical with those for the corresponding model chain. The complexation behavior and complex structures are characterized through laser light scattering and atomic force microscopy measurements. The order of the apparent weight-averaged molar mass and the order of density of complexes observed from the three experimental systems are qualitatively in agreement with those predicted from the simulations.

The interfacial properties for a carbon nanotube on a Ni (001) surface are modeled by a piece of vertical graphene standing on a Ni (001) surface. The interaction between the graphene and the nickel (001) surface is investigated using density functional theory (DFT) calculations. Zigzag type graphene can stand on the hollow sites of the Ni (001) surface along the [linear span]110[linear span] direction. For such a configuration, Ni (001)-graphene interfacial mechanical properties are studied, and we find that Ni-Ni bonds near the interface will break first under tensile strain. C-C bond lengths near the interface are longer than the C-C bonds of graphene, and the charge density of those bonds decrease due to the formation of interfacial Ni-C bonds. It suggests that C-C bonds near the interface may break during the carbon nanotube growth processes.

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